1. Field of the Invention
This invention relates to an auxiliary device for an automobile brake system, and more particularly to an anti-lock braking control device for a hydraulic brake system of an automobile.
2. Description of the Related Art
At present, anti-lock braking systems have been widely used in automobiles for ensuring safety when driving. Generally, the anti-lock braking systems are controlled either by an electronic device or a mechanical device. The anti-lock braking system of the electronic type is very complex and has a computer and sensors which are installed in each wheel to detect the occurrence of a skid or lock-Up condition. In an example of the prior art, information that sensors gather causes a high pressure hydraulic pump to reduce the pressure in the wheel that is just about ready to skid. In this manner, the wheels are allowed, in a controlled fashion, to be relieved of pressure from the brake shoe or pad in order to rotate again, albeit in a very short period of time. As soon as the wheels start to rotate, the computer again controls the hydraulic pump to apply pressure to the brakes in order to stop the wheels from rotating. This sequence is repeated normally at a rate of 4 times/second. It is known that the maximum braking action is achieved just before the wheels skid on a surface. Such an electronic type anti-lock braking system is expensive due to its complexity.
In another case, the anti-lock braking system of the mechanical type is controlled by a brake rubber member which is installed in a closed chamber. Specifically, when the brake pressure exceeds a predetermined value, the brake rubber member will deform or expand to increase its volume, thereby reducing the braking pressure in the brake lines in order to prevent the wheels from being locked up. When the brake rubber member is retracted to its original state, the brake pressure in the brake lines are increased to prevent the wheel from rotating. This sequence is repeated to achieve an intermittent braking effect, as described above. The anti-lock braking system of the mechanical type is simple in structure, is easy to install in an automobile hydraulic brake system, and is relatively inexpensive to manufacture. However, because the response of the brake rubber member is much slower that of the electronic devices, the response of the mechanical type anti-lock braking system is poorer than that of the electronic type anti-lock braking system.
Therefore, there is a need for an anti-lock braking system which has a simple structure and a quick response for effecting the intermittent brake action.